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CS307 Operating Systems
Operating-System Structures
Fan Wu
Department of Computer Science and Engineering
Shanghai Jiao Tong University
Spring 2012
A View of Operating System Services
Operating systems provide an environment for execution of
programs and services to programs and users
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Bourne Shell Command Interpreter
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First GUI (1973)
The first appeared
on the Xerox Alto
computer in 1973.
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Mac OS System 1.0 (1984)
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Amiga Workbench 1.0 (1985)
The first GUI with color graphics.
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Windows 1.0x (1985)
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IRIX 3 (released in 1986, first release 1984)
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NeXTSTEP / OPENSTEP 1.0 (1989)
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Windows 95 (1995)
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KDE 1.0 (1998)
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GNOME 1.0 (1999)
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Windows XP (released in 2001)
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Windows Vista (released in 2007)
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Mac OS X Leopard (released in 2007)
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KDE (v4.0 Jan. 2009, v4.2 Mar. 2009)
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A View of Operating System Services
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System Call
 Programming interface to the services provided by the OS
 Typically written in a high-level language (C or C++)
 Example: System call sequence to copy the contents of one file to another
file
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API
 Mostly accessed by programs via a high-level Application Program
Interface (API) rather than direct system call use
 Three most common APIs

Win32 API for Windows
 POSIX API for POSIX-based systems (UNIX, Linux, and Mac OS X)
 Java API for the Java virtual machine (JVM)
 Why use APIs rather than system calls?

Program portability
 System calls are often more detailed and difficult to work with than the
API
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Example of Standard API

Consider the ReadFile() function in the

Win32 API—a function for reading from a file

A description of the parameters passed to ReadFile()

HANDLE file—the file to be read

LPVOID buffer—a buffer where the data will be read into and written from

DWORD bytesToRead—the number of bytes to be read into the buffer

LPDWORD bytesRead—the number of bytes read during the last read

LPOVERLAPPED ovl—indicates if overlapped I/O is being used
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API – System Call – OS Relationship
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Standard C Library Example
 C program invoking printf() library call, which calls write() system call
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Examples of Windows and Unix System Calls
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A View of Operating System Services
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Operating System Services

Operating-system services:

User interface - Almost all operating systems have a user interface (UI).

Graphics User Interface (GUI), Command-Line (CLI), Batch

Program execution - The system must be able to load a program into memory
and to run that program, end execution, either normally or abnormally (indicating
error)

I/O operations - A running program may require I/O, which may involve a file or
an I/O device

File-system manipulation - Programs need to read and write files and
directories, create and delete them, search them, list file Information, permission
management.
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Operating System Services (Cont.)

Communications – Processes may exchange information, on the same
computer or between computers over a network


Communications may be via shared memory or through message
passing (packets moved by the OS)
Error detection – OS needs to be constantly aware of possible errors

May occur in the CPU and memory hardware, in I/O devices, in user
program

For each type of error, OS should take the appropriate action to
ensure correct and consistent computing

Debugging facilities can greatly enhance the user’s and
programmer’s abilities to efficiently use the system
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Operating System Services (Cont.)

Resource allocation - When multiple users or multiple jobs
running concurrently, resources must be allocated to each of
them

Accounting - To keep track of which users use how much and
what kinds of computer resources

Protection and security - The owners of information stored in a
multiuser or networked computer system may want to control
use of that information, concurrent processes should not
interfere with each other
 Protection involves ensuring that all access to system
resources is controlled
 Security of the system from outsiders requires user
authentication, extends to defending external I/O devices
from invalid access attempts
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CS307 Operating Systems
Operating-System Structure
Simple Structure
 MS-DOS – written to provide the most functionality in the least space

Not divided into modules

Although MS-DOS has some structure, its interfaces and levels of
functionality are not well separated
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Traditional UNIX System Structure
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Layered Approach
 The operating system is divided into a number of layers (levels), each
built on top of lower layers. The bottom layer (layer 0), is the
hardware; the highest (layer N) is the user interface.
 With modularity, layers are selected such that each uses functions
(operations) and services of only lower-level layers
 The main advantage of the layered approach is simplicity of
construction and debugging
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Microkernel System Structure
 Moves as much from the kernel into “user” space
 Communication takes place between user modules
using message passing
 Benefits:

Easier to extend a microkernel

Easier to port the operating system to new
architectures

More reliable (less code is running in kernel
mode)

More secure
 Detriments:

Performance overhead of user space to kernel
space communication
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Mac OS X Structure
(Darwin)
Modules
 Most modern operating systems implement kernel modules

Uses object-oriented approach

Each core component is separate

Each talks to the others over known interfaces

Each is loadable as needed within the kernel
 Overall, similar to layers but with more flexibility
 Like microkernel but more efficient
Solaris Modular Approach
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Virtual Machines
 A virtual machine takes the layered approach to its logical conclusion.
It treats hardware and the operating system kernel as though they
were all hardware.
 A virtual machine provides an interface identical to the underlying bare
hardware.
 The operating system host creates the illusion that a process has its
own processor and (virtual memory).
 Each guest is provided with a (virtual) copy of underlying computer.
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Virtual Machines (Cont.)
(a) Nonvirtual machine
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(b) virtual machine
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Architecture
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Benefits of Virtualization
Before Virtualization
After Virtualization
• Multiple OSs on a single machine
• Hardware-independence of operating
system and applications
• Better utilization of resources
• Encapsulating OS and application into
virtual machines
• Single OS image per machine
• Software and hardware tightly coupled
• Underutilized resources
• Inflexible and costly infrastructure
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Virtual Infrastructure for Data Center
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Amazon Elastic Compute Cloud (EC2)
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The Java Virtual Machine
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Homework
 Reading

Chapter 2: Operating-System Structures
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